@MrHau 

Make sure your Intvernet port has the appropriate speed:

If your Internet port is capped at 100 mbps then check these settings:

@MrHau 

Hello, is the speed back to normal after the reset?

MrHau wrote

Have made reset and is back to normal, but then second day is again drop to 100 WiFi and lan both, now have reset router again will look inside setting if drop again

@MrHau 

Thanks for getting back.

May I know who is your ISP? Before the firmware update, there was no issue? We would like to escalate your case to our engineers, the engineering team will investigate to see if it is a concern in the router that can be resolved.

@MrHau 

Thank you. I've forwarded your email address to the engineering team for a follow-up. 

@MrHau 

Regarding the "This network is blocking encrypted DNS traffic" message, we share what we have confirmed.

Ever since iOS 14, Apple started supporting encrypted DNS, and sometimes you might get this“ privacy warning: this network is blocking encrypted DNS ” notice on your iOS devices when they are connected to a network that did not support encrypted DNS. The Archer routers don't support encrypted DNS now, but they can forward the traffic to the DNS servers without an issue.

Try figuring this out, you can try the following:
1. Go to the Wi-Fi Settings of your iOS devices, forget/delete the network, then reconnect to it again. Check and confirm if the privacy warning will disappear.
2. If that doesn't help, try changing the DNS servers on the router to 8.8.8.8 and 1.1.1.1 (Under Advanced > Network > Internet) manually, then go to the Wi-Fi Settings of your iOS devices, forget/delete the network, then reconnect to it again.